Documents become slow once added to a book, even just scrolling through the document

I am working on a book with fairly complex documents. InDesign was running slow and was crashing, so somewhere while working on the book I had to reset my preferences. All the documents in the book were still pretty slow/laggy, but I figured that was just because they had a lot going on (many different styles, images, cross-references, captions, etc.). But now I think the problem is with the book itself. Today I worked on a new chapter, and InDesign worked quickly and smoothly for the entire layout. When I was nearly finished doing the layout, I realized I had forgotten to add the document to the book file, so I went ahead and added it at the end. I updated all numbers for the book, and then when the numbers finished updating I went back in to do a final lookover and fix any mistakes.

Performance immediately dropped to barely a crawl. Even just scrolling through the document was janky and slow. Actually making any changes to the document, even small ones such as replacing a single character, took over a minute. As soon as I type to make the change, my cursor turns into an hourglass. After about fifteen seconds or so, I will see the loading box with the blue bar (such as you usually see when InDesign is running a long Find and Replace, or updating numbers) come up for a split second, but there is no text in that box to indicate what is loading. The loading box will appear for a split second roughly every fiteen seconds, until finally the change is made.

Usually when InDesign does something like this it's because it's reflowing all the text or making a large change to the book, but sometimes it's triggered when I'm not making any changes. This chapter is at the end of the book and shouldn't affect numbers in previous documents. Furthermore, I even removed the document from the book completely, and even deleted the book file, and my document is still running with poor performance.

This is utterly unworkable considering making very minor changes takes over a minute. My guess is that whatever was going on before that required me to reset my preferences is somehow baked into the book file, which has in turn baked it into all the documents it contained since the book file itself is now deleted.

Does anyone have any idea how to fix this? Or how to prevent it from happening again? I have tried saving to idml, but that has not made a difference.